Cleaning and preservation of metallic surfaces



l. UUIYH'UDI HUNG,

reti ed Patented Oct. 31, 1933 UNITED STATES 1,932,553 PATENT OFFICECLEANING AND PRESERVATION OF METALLIC SURFACES George L. Magoun, Nitro,W. Va., assignor to The Rubber Service Laboratories Compam", Akron,Ohio, a corporation of Ohio No Drawing. Application January 19, 1931Serial No. 509,884

8 Claims.

The present invention relates to the cleaning and preservation ofmetallic surfaces, wherein the metal is in contact with a liquid of anacid nature. More particularly, the invention relates to the preventionof excessive pitting and embrittlement of ametal when subjected to apickling process by treatment with a dilute solution of a non-oxidizingacid.

Certain objects of the present invention are to prevent the acid pickleliquor from attacking clean portions of the surface of a metal; toobviate over-pickling, embrittlement and pitting of the articlestreated; to minimize the amount of metal lost in pickling; to increasethe efiiciency of the pickling operation; to prolong the effective lifeof the pickling bath; and particularly to facilitate the picklingoperation. Other and further objects of the invention will be apparentfrom the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid toremove oxides such as rust, scale, and other deposits. after which themetal is preferably washed with water and dipped into an alkaline bathto remove the last traces of free acid. The acid removes the rust andscale, but unfortunately, from the pickling standpoint, unless someagent to prevent such action is present, it g ttacks the cleaned metalitself, thereby .causin l ss of metal and producing an evolution ofhydroge'n'gas, which escapes into the air, carrying with it a fine sprayof the acid liquor from the pickling bath and producing an atmospherepossessing corrosive properties and one which is injurious to health anddamaging to equipment.

By the present invention, these objectionable features of the picklingprocess are substantially overcome or reduced to a minimum. Toaccomplish the objects set forth in accordance with the presentinvention there is added to the pickling bath a regulating agent oringredient which acts to restrain the action of the acid from attackingclean metal but facilitates the removing of rust, scale and otherdeposits, or in other words the regulator or inhibitor causes the acidselectively to remove such materials without appreciably attacking theclean portions of the metal under treatment.

The pickle regulator or inhibitor, as disclosed in the presentapplication, comprises a reaction product of a fully saturated organicbase and a mercaptoarylthiazole.

In the examples hereinafter set forth for carrying out the metalpickling process, conditions were imposed which duplicated, so far aspossible, those commonly followed in commercial practice, so far asconcerned acid concentrations and temperatures employed.

Test pieces of 30 gauge cold rolled tin plate steel stock, approximately4" x 3" in dimension, were immersed in approximately 750 c. c. of awater solution of sulfuric acid containing approximately 6% by weight of66 B. acid to which had been added a small quantity of one of thepreferred type of inhibitors. The loss in weight of the steel testpieces resulting from maintaining the strips in the pickle bath in themanner described for a definite period of time was then determined. Thetemperature of the pickling bath was maintained at from 80 to 85 C. Forthe acid concentration set forth, commercial practice is to pickle atapproximately 66 to 88 C. The results so obtained were compared withsimilar tests wherein the steel pieces were subjected, under theconditions set forth, to the action of an acid solution of the strengthand for the time specified above, but containing no inhibitor.

One of the preferred class of compounds, for example, a reaction productof hexamethylene tetramine and 2-mercaptobenzothiazole, was prepared byplacing approximately 175 parts by weight of hexamethylene teiramine andapproximately 313 parts by weight of Z-mercaptobenzothiazole in asuitable vessel, mixing and heating the contents to a temperature ofapproximately 90 to 135 C.

A sample of the product prepared as described above was incorporated ina pickling bath in the manner hereinbefore described. Thus, a steel testpiece, 3" x 4 in dimension, cut from 30 gauge cold rolled tin platestock, exposing approximately 24 square inches of surface and weighing18.230 grams, was found to lose but 0.019 grams after 40 minutespickling in 750 c. o. of a 6% sulfuric acid solution containing 0.047grams of the inhibiting product hereinbefore described. A similar testpiece weighing 18.738 grams and treated in the same manner, but withoutthe use of any inhibitor lost 0.541 grams. Thus it is shown that whenthe reaction product of hexamethylene tetramine andZ-mercaptobenzothiazole is employed as an inhibitor, the loss in weightper square inch of surface exposed corresponds to 0.00079 grams, whereaswhen no inhibitor is employed in the test described, the loss per squareinch of surface exposed corresponds to 0.0225 grams. The loss in weightper square inch of surface exposed is only 3.5 per cent as great byemploying the inhibitor set forth as results if no inhibitor is employedin the pickling process. A greater saving in metal losses results fromthe use of a larger amount of the inhibitor than that employed in theexample. Moreover, the steel plates pickled in the presence of theinhibitor set forth are clean and not stained upon removal from thebath.

Other mercaptoarylthiazole derivatives of saturated organic bases havebeen prepared and tested. Thus the following reaction products have beenprepared and tested in a manner analogous to that hereinbefore setforth. With the exception of compounds E and F, the methods for thepreparation of which are given below, the following reaction productswere prepared in a manner analogous to that hereinbefore described forthe preparation of the reaction product of hexamethylene tetramine andmercaptobenzothiazole.

Compound A.--Reaction product of substantially one molecular proportionof Z-mercaptobenzothiazole and substantially one molecular proportion ofdiethylamine.

Compound B.Reaction product of substantially one molecular proportion of2-mercaptobenzothiazole and substantially one molecular proportion oftriethanolarnine.

Compound C.-Reaction product of substantially one molecular proportionof Z-mercaptobenzothiazole and substantially one molecular proportion ofpyrrolidine.

Compound D.-Reaction product of substantially one molecular proportionof Z-mercaptobenzothiazole and substantially one molecular proportion ofpipgridine.

CompoundE-l-teaction product of substantially two molecular proportionsof 2-mercapt0- benzothiazole and substantially one molecular proportionof acetaldehyde-ammonia. (The reaction was accomplished in this case byheating the mixture of the reactants at approximately 150 to 160 C. fora period of approximately two hours.)

Compound F.-Reaction product of substantially one molecular proportionof bis-mercapto benzothiazole and substantially two molecularproportions of tributylamine. (The reaction was accomplished in thiscase by heating the reactants in an alcoholic solution.)

The results of the tests obtained on immersing steel test strips of 30gauge cold rolled tin plate stock, 3" x 4" in dimension, for 40 minutesin 750 c. c. of 6% by weight of 66 B. sulfuric acid at C., in thepresence of 0.04? grams of one of the above described inhibitors, aregiven in Table I.

Table I W ight 10$ Inhibiting Weight of 229 in grams per compoundinhibitor i p square inch of employ ed employ ed Diem-m" pickling GramsGrams Grams Grams Compound A 0. 047 18. 7'. 18. 762 0. 00042 Compound 130. (ii? 18. T75 18. 763 0. 00050 Compound C 0. 047 i8. 305 18.2660.00103 Compound D. 0.047 18.905 18.865 0.00l67 Compound E- 0. 0 .717.448 14. 429 0. 00079 Compound F 0. 47 18.606 i8. 563 0.00175 NoneNone. 18.738 18.197 0.02254 It is thus apparent from the data set forththat the preferred class of materials constitutes an important andhighly efiicacious group of inhibitors, as in all cases wherein one ofthe preferred inhibiting compounds was incorporated in the pickle liquorthere resulted a great saving in the loss in weight of the steel teststrips as compared with that resulting when no inhibitor was employed.

As a further example of operating the present invention, the reactionproduct of substantially one molecular proportion ofZ-mercaptobenzothiazole and substantially one molecular proportion ofmorpholine was prepared and tested in the pickling bath as an inhibitorin the manner hereinbefore described, and it was found to possess theinhibiting qualities of the preferred class of compounds.

In like manner, other fully saturated organic bases, such asdiethanolamine. cyclohexylamine, ethanolarnine, diacetone-amine, andpropylamines, may be reacted with mercaptobenzothiazoles,mercaptotolylthiazoles, and the like and the product so obtainedemployed as inhibitors.

Other modes of employing inhibitors of the class hereinbefore set forthin the acid pickling of metals are apparent to those skilled in the artto which this invention pertains. The products described additionallymay be employed in the presence of foaming agents, ionizable sub stancesor other materials ordinarily used, and are employable with the variousacids commonly employed commercially in the acid pickling of metals.

What is claimed is:

l. A process of pickling iron and steel products which comprisessubjecting the metal to be pickled to the action of a sulfuric acidsolution containing a small proportion of a reaction product of a fullysaturated aliphatic amine and a mercaptobenzothiazole.

2. A process of pickling iron and steel products which comprisessubjecting the metal to be pickled to the action of a sulfuric acidsolution containing a small proportion of a reaction product of a fullysaturated aliphatic tertiary amine and a mercaptobenzothiazole.

3. A process of pickling iron and steel products which comprisessubjecting the metal to be pickled to the action of a sulfuric acidsolution containing a small proportion of a reaction product ofhexamethylene tetramine and 2-mercaptobenzothiazole.

4. A process of pickling iron and steel products which comprisessubjecting the metal to be pickled to the action of a sulfuric acidsolution containing a small proportion of the product formed by reactingsubstantially 175 parts by weight of hexamethylene tetramine withsubstantially 313 parts by weight of Z-mercaptobenzothlazole.

5. A pickling bath for iron and steel products which comprises asulfuric acid solution containing a small proportion of a reactionproduct of a fully saturated aliphatic amine and amercaptobenzothiazole.

6. A pickling bath for iron and steel products which comprises asulfuric acid solution containing a small proportion of a reactionproduct of a fully saturated aliphatic tertiary amine and amercaptobenzothiazole.

7. A pickling bath for iron and steel products which comprises asulfuric acid solution containmg a small proportion of a reactionproduct of hexamethylene tetraminc and 2-mercaptobenzotbiazole.

8. A pickling bath for iron and steel products which comprises asulfuric acid solution containing a small proportion of the productformed by reacting substantially 175 parts by weight of hexamethylenetetramine with substantially 313 145 parts by weight ofZ-mercaptobenzothiazoie.

GEORGE L. MAGOUN.

CERTlFlCATE OF CORRECTION. October 31, 1933.

'Patent No. 1,932,553.

GEORGE L. MAGOUN.

It is hereby certified that error appears in the printed specificntionof the above numbered patent requiring correction as follows: Page 2,line 59, column for "0.47" read 0.047; and that the said Letters Patentshould .2, of Compound F,

hat the same may conform to the'r'ccord of be read with this correctiontherein t the case in the Patent Office.

Signed and scaled this 12th day of December, A, D. 1933.

i. M. Hopkins (Seal) Acting Commissione of Patents.

